title: Analysis of the Escherichia coli ribosome-ribosomal subunit equilibrium using pressure-induced dissociation.
abstract: Hydrostatic pressure can be used to perturb the ribosome-ribosomal subunit equilibrium. We have used glutaraldehyde fixation and subsequent sucrose gradient analysis to determine the equilibrium concentrations of Escherichia coli 70 S, 50 S, and 30 S particles at pressures from 1 to 1400 atm. This method is shown to be sufficiently rapid and free of interfering ribosomal aggregation artifacts when performed at Mg2+ concentrations below 8 mM. We show directly that the E. coli ribosome is in equilibrium with its subunits and that the pressure-sensitive reaction is appropriately described by the expression: In Kp = ln K0 + (P delta V/RT), where Kp and K0 are the equilibrium constants at pressure P and 1 atm, respectively, and delta V is the change in molecular volume that occurs during the reaction. The method provides values for K0 under different conditions, and the effects of Mg2+ ion can be readily ascertained. K0 and delta V were also estimated by a method of fitting computer-generated sucrose gradient profiles to experimental profiles. Determination of delta H0, delta S0, and delta V0 at 5 mM Mg2+ are presented. The results are discussed in the context of previous thermodynamic studies of the E. coli ribosome.
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D005976:Glutaral; D008274:Magnesium / Q000494:pharmacology; D009994:Osmolar Concentration; D011312:Pressure; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D008274:Magnesium; D005976:Glutaral